The AM Forum

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I  recall there used to be a product called Glyptal, a high voltage paint.  It came in either red or black.  I  would assume the black stuff used something other than carbon black for pigment.  In fact, I tried to find some a few years ago, but all I could find was the red stuff.

You  can't lose anything by trying out the transformer.  If the paint is in fact pigmented with carbon black, the transformer is ruined anyway, so you won't lose anything when it craps out.  If it holds up, it is probably impregnated with the black Glyptal or something like it.

Have you contacted the seller to see if he knows anything about this?  Is this a newly manufactured transformer or a "refurbished" one?

yeah how weird, what's the story on this one?

I've seen black paint applied to the windings of a few audio transformers on tube sound reinforcement amps I have worked on. Not sure why it was used over the varnish on the windings, but it was not problematic. What you received might work fine.

On the other hand, a Thordarson CHT 300 is nothing to sneeze at! Mine has been happily and reliably handling audio duties in my medium powered rig for 30 years and who knows what it went through before it landed here. It's a great sounding transformer!

Rob W1AEX

I've plenty of black-painted transformers in high powered transmitters for many years.  Electro Engineering, Westinghouse, and Basler Electric come to mind right off. 

None of it even looked like Glyptal varnish, too thin.

Run what you brung, as they say. ;)

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the thor CHT 300 watt unit TM-77 was what the first HB rig used,  with 805's.  I've never seen the TM-78 500 watt version. trouble is the plugs for the plug n jacks are always missing.

Its not a paint and has been used that way for decades on Peter Dahl and other transformers. Im looking at an original late 70's Dahl Alpha 77SX xfmr as I type this.

Instead of starting a panic mode thread it would make more sense to call Magcap and get an edumencation ::).

Carl
KM1H

why dont you call them on the phonium and voice your concerns? I dont think they would purposely sell a defective product.

and are you talkin about the people that took over Peter Dahl?

If you can't get any information, I would at least HI-POT test it or find an electrician that will lend you an insulation tester to check it out. If it HI-POTs at 5KV with out any problems, chances are it will be FBOM.

Signal Transformer co. uses black paint or whatever the coating is and i have never seen one fail

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The "Signal Transformer Corporation" has made black transformers for decades. The black does penetrate into the magnet wire. More recently the EPA and OSHA folks are regulating transformer varnishing processes. The signal folks describes the 3 main varnishing / potting categories used today.

Here is the link:


http://www.signaltransformer.com/TechnicalLibraryPage.asp?pDoc=20

Jim
WD5JKO

Is this a newly manufactured transformer or something purchased from NOS? Who is the manufacture? Is it a multi tap? I would like to see a picture if possible.

Easy to find: go to your neighborhood Shadio Rack, and buy  a package of cheap RCA plugs.   Take 'em apart and keep the pins and attached phenolic ring, and junk the outer part. Presto!  Thordarsen Plugs!

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Seems sillly not to call the company... 99% chance they know what they are doing, and have hipot tested the product before shipping.

If it was my rig, I'd install it and let it rip.

If it arcs, then I'd call them up and send it back for a free re-do.

But that's only my opinion.

                           _-_-bear

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Shouldn't be a concern.

There's only a few volts between turns of even high voltage transformers.

  You have a good point there. The CHT is now in and working fine. Will vacuum varnish the new tranny and use it later on.

The greatest danger is from arcing over between layers of windings, and between the windings and the core of the transformer.  Also, the manufacturer sometimes failed to sufficiently insulate the leads running to and from the windings, from the rest of the winding and/or the core.  If there is no varnish or other treatment, moisture from the air can degrade the insulation, particularly the kind of paper used in older transformers.  The paper itself degrades over time and becomes brittle and undoubtedly a less perfect insulator even if it is kept dry.

That's why I always float the frame of vintage modulation transformers, modulation reactors and filter chokes away from ground and make sure I am using well insulated mounting hardware.  It is not a good idea to impose unnecessary HV stress on whatever dielectric exists between windings and core.

This should be less a problem with newly constructed transformers.  The insulating materials used to-day are supposed to be far superior to what was used in the WW2 era and before.

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Here's the dielectric properties of Glyptal transformer varnish.
There's at least a dozen places selling it per Google.

You can also still get Q-Dope and Scotchkote as alternatives.

Typical Glyptal Cured Film Properties:
Dielectric strength—Dry—ASTM 0115-55—volts/mil 1500
Dielectric strength 24 hours in water—volts/mil 350
Arc resistance—seconds 480

 Meets requirements of MIL-E-2218
 Flexibility is far superior to competitive red sealers on both backed and air-dried films. 1201 can take rugged impact.
 Water Resistance is excellent.
 Prolonged Aging doesn’t crack 1201’s film, leaves no place for destructive agents to get in.
 Drying 1201 is tack-free in about 2 hours at room temperature, can be baked to a beautiful smooth finish.
 Heat Resistance. 1201 has got it, can withstand continuous 135°C temperatures.
 Toughness. High-gloss paints have a tender film. 1201 has a low-gloss finish, designed for great resistance to abrasion.
 Adhesion. 1201 hangs on, stays where it’s put—on metals, ceramics, porcelain, concrete, fibres, and wood.

also tried to add Don's quote about Glyptal color .... GE used the stuff ( usually green ) for many years after alignment to keep vibration from shifting settings .... fwiw ...73

I believe that Collins used the red Glyptol on the S-line/ KWM series as a QC marker for solder joints that were checked and approved. I have a 75S-3B loaded with it under the chassis. Perhaps to keep atmosphere from the joints?

i've seen many HV transfomas painted black. I never bothered to check ot what kind of paint it was.

however I dont think the black pigment would make much of a difference if the outpoot terminals have a little space between them. The Big Gates transformer That I have is painted black (open frame). The one that came from Timtron (8kv ct) is painted black. The one in Derb's leanyour is painted black, and most ot the generic
(non applicatiom specific) stuff I have seen from Peter Dahl was painted black.

Even if the pigment was ever so slightly conductive, the small amount of it and the spacing of the high side outpoot terminals, should render it ineffictive and the flashover leakage should render it negligible.

If at all possible, with older open framed transformers, I like to "bake" them at 190-200 degrees for 8-12 hours to expel any moisture that may have gotten into the insulation, and while they are still hot, drop them into a bucket of old oil-based varnish to cool. this way as they are cooling they will draw the varnish into the windings as they cool. Let them soak for a few days and then pull them out to "drip dry". After they have dried to the touch (usually a couple days) dunk them again.
I will gige them several dunkings untill they look like a glazed donut. Let them sit for a few months to dry thoroughly and return them to service. A second "baking" at a lower temp will expedite the final drying process, but so will a fwe days sitting out in the hot summer son.

                                                  The Slab Bacon

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did we call the factory and inquire yet??   ::)

It could be an error due to a new "employee" on the line?? ...does happen...

               _-_-bear